Oscillation generator and frequency multiplier



Jan. 18, 1949. A. P. BUFFiNGTON OEICITJII'JNI'ION GENERATOR ANDFREQUENCY MULTIPLIER Filed Mafch 15, 1946 MULT/PL/ER do I - mama/var(MEG/VCYCLES) INVENTOR. HAHN P. BUF'F/NGTUN Patented Jan. 18, 1949UNITED OSCILLATION GENERATOR AND FREQUENCY MULTIPLIER Alan P.Buflington, Philadelphia, Pa., assignor, by mesne assignments, to PhilcoCorporation, Philadelphia, Pa., a corporation .of PennsylvaniaApplication March 13, 1946, Serial No. 654,046

7 Claims. (01. 250-36) This invention relates to improvements infrequency multipliers, and particularly to improvements in frequencymultipliers of the type driven directly by an oscillator. The inventionhas been found to be applicable but is not limited to the combination ofan oscillator and a frequency multiplier employing a single dual-purposevacuum tube, as for examplea double triode, which functions both as theoscillator and as the frequency multiplier.

It has long been conventional to use the superheterodyne principle inthe amplification of received amplitude-modulated carrier wave signals,and it is equally conventional to. use this principle in theamplification of received frequency-modulated signals. As is well known,superheterodyne receivers customarily employ a local oscillator forsupplying the heterodyning frequency used by the mixer or converter tubein the process of converting the frequency of the carrier signals to anintermediate frequency which is more conveniently amplified.

Under recently prescribed regulations, the broadcast offrequency-modulated signals in the United States is assigned to thefrequency band extending from 88 to 108 megacycles. This band is veryhigh in comparison with the amplitudemodulation broadcast band whichextends from 550 to 1600 kilocycles, and it is also substantially higherthan both the AM short wave band (upper assigned limit approximately 22megacycles) and the heretofore employed FM band (42 to 50 mo.).

The generation of local oscillations over the range of frequenciesrequired for heterodyning with the recently assigned very high FMcarrier band presents difiiculties which were not present to anyappreciable extent at the lower frequencies heretofore used' Thesedifficulties may be reduced, but not altogether avoided, by the knownexpedient of employing an oscillator in combination with a frequencymultiplier, the oscillator being operated at a sub-harmonic of the localfrequency required for heterodyning, while the required high frequencyoscillation is obtained from the output circuit of the frequencymultiplier.

A frequency-modulation receiver employing an oscillator-multiplier inplace of the more conventional fundamental-frequency oscillator isdisclosed in the co-pending application of Milton L. Thompson, filedDecember 7, 1945, Serial No. 633,453, and assigned to the assignee ofthe present invention. While the arrangements therein disclosed areproductive of very substantial improvements in the frequency stabilityof the locallygenerated oscillations, it has been found that frequentlythe voltage output of the multiplier section of prior, tunableoscillator-multiplier circuits is neither large enough nor uniformenough for satisfactory performance of the receivers frequency converterstage.

The output voltage obtainable from a frequency multiplier is known to beinversely proportional to the order of the selected harmonic.Consequently, in order to secure as high an output as possible,frequency multipliers are preferably employed to generate the secondharmonic, rather than the third or higher harmonics, and as sucharecommonly referred to as frequency doublers. In the case of asuperheterodyne FM receiver, assuming that an intermediate frequency ofthe order of 9 megacycles is to be employed and that the localoscillation frequency is to be on the low frequency side of the receivedsignal, it will be necessary for the oscillator section of theoscillator-doubler'to generate oscillations having frequencies tunableover the range extending from about 39 to 50 megacycles. The doublersection will accordingly deliver local oscillations whose frequenciesare variable over the second harmonic range extending from '78'to me.The cause or causes of low and non-uniform doubler output voltage atthese very high frequencies'are difiicult to determine. Among thefactors involved is the fact that at high frequencies the inductivereactances of the leads between the various circuit components areappreciable in comparison to the reactance values of the circuitcomponents themselves, and this is true even though the leads be kept asshort as possible. Moreover, stray capacitances exist between the leads,the circuit elements, the tube electrodes, the chassis, etc., the valuesof which at these high frequencies are sufficient to affect seriouslythe operation of the apparatus. For these and other reasons, theoperation of very high frequency apparatus is diflicult to analyseaccurately.

It will be understood by those skilled in the art that the localoscillation voltage introduced into the mixer or converter tube of asuperheterodyne receiver is preferably held approximately con-' plitudeof the local oscillator wave with respect to that of the inlcQming'R-F.carrier wave. For

R.--F. carrier wave.

amplitude of the difference-frequency component 3 linear detection, theamplitude of the local oscillation should be much greater than that ofthe Where this is the case, the

of the mixer tube output is largely independent of the amplitudeof thestrongerv local signal,.and nearly proportional to the strength of theweaker incoming carrier signal. And the magnitude of thedifference-frequency output is largest when:

the amplitude of the stronger component differs from the amplitude ofthe weaker'signal by the greatest amount.

In a preferred form of the present invention, improvements are madein-high frequency oscillator-multiplier circuits which efi'ect"-asubstantial increase in the amplitude of the multiplier -,V includesgrid capacitor ;l2',. grid leak: l3, paravsiticsuppressingresistor-14,:a part of inductance coil 5, conductor 25, and the ground lug 8, thecircuit to cathode H being completed through chassis.

1 The-signal developed at grid of the oscillator portion of tube V isapplied directly to grid l6 output voltage and which also attain asubstana tial improvement in the uniformity of the amplitude over thefrequency range.

In another form of the present invention, improvements are made in highfrequency oscillator-multiplier circuits which'cause the amplitude ofthe output voltage of the frequency multiplier to be more uniform inmagnitude over the required frequency band without necessarilyaccomplishing increase in the'amplitude.

It is an objectof this invention to providein combination a highfrequency oscillator and a frequency multiplier, the frequencymultiplier having improved uniformity of output voltage over theoperating frequency range.

It is another object of thisinvention to provide a high frequencyoscillatorin combination with a frequency multiplier, where in thefrequency multiplier has substantially increasedoutput volt age, as wellas improved uniformity of output voltage over the operating frequencyrange.

It is a more specific object of this invention to provide a highfrequency, oscillator-multiplier having external coupling arrangementsbetween the output circuit of the frequency'multiplier and the circuitsof the oscillator whereby :high fre-. quency energy may be-fed back fromthe .multi-. plier to theoscillator to thereby achieve increasedmultiplier output and improved uniformity thereof over the operatingfrequency range.

These and other objects'and advantages of the present invention, as wellas the invention itself; will be best understood by reference to thefol-- lowing description and accompanying drawings wherein i Figure l isa schematic illustration of a preferred form of circuit organization forcarrying my invention into effect; and

Figure 2 illustratesby means of a graph, the scope of the improvementswhich are realized from the invention. o

Referring now to Figure 1, there is schematically illustrated a highfrequency oscillator-fre-. quency-multiplier in which theoscillatorportion is tunable to a sub-harmonic of the desired localoscillationfrequency by means of the oscillator frequency-determining circuit Icomprised of variable tuning capacitor 2, trimmer capacitor ,3, andinductance coil or winding 4. The latter is inductively coupled to coilor winding 5 as shown. Vacuum tube V, which may be a commercial type TF8tube, is comprised of two triode sections, one of which functions as.theoscillaton. .As shown in, the,.;figure, the external circuitconnections of the oscillator include a plate circuit comprised of,

coupling capacitor 6, a part of i-nductance coil conductor (which,physically, is verys-hort), and groundlug 8 of frequencymultiplier tangocircuit v I 0, the return to the =-cathode .;l.l being;

of the second triode-section of the tube' This secondsection of tube Vfunctions as the frequency multiplier and is tunable to the desiredharmonic of the oscillator frequency by frequency-determining circuit H)which is comprised of variable tuning capacitor I1, trimmer capacitorIB'and' inductance coil 9. For maximum multiplier output, circuit I0 ispreferably tuned to the second harmonic of the frequency generatedin theoscillator portion of the apparatus, and for convenience of operationtuning capacitors 2 and "may be ganged together by known'mechanicalmeans. 7

Assuming that the apparatus illustrated "in Figure 1 is to function asan oscillator-doubler and is to be employed to supply the heterodyningfrequency in a frequency-modulation receiver iof the superheterodynetype, the operating frequency 'of-the oscillator may be made-variabla-bymeans of the tuning/capacitortZ over a range extending from about.39t'o' 50 megacyclesnThe frequency-doubler portionof the apparatusisis;accordingly, tunable by meanslof. the capacitor I! over a rangeextending; fromnabou't 718 toi 10 0 megacycles, thusproviding coverage.ofsaiband 7 extending from about 87*to 109. mega'cycleswhen anintermediate frequency of 9 mBg-ECYCIBSF-iSEm ployed. The tunedoscillator and doubler circuits should, of course, trackaccuratelythroughout their tunable ranges.

The output voltage of the multiplier may :be taken from coil 9,?as forexample, from tap 19', and may if :desired be applied through conductor20 directly to a control electrode of the converter tube of asuperheterodyne receiver (not shown).

Ifthis is done; the most desirable. tap point' onz' coil 9 willbedetermined byithe impedance-50f. the converter tube into which themultiplieno ute put voltage is injected. V

Coupling .zcapacitor 2| isolates the ,--multiplier tank circuit from thehigh D.-C. voltage applied to the anode of the multiplier triode, whilepro viding-thernecessary R.-F. .couplinghgtw i anode andsaid tankcircuit. Resistor 22 and choke coil 23,.are effective to isolate thetunedradio. frequency circuits; from B+. If desired; both 'of'theseisolating elements maybe choke coils, or both may be resistors.

.In the conventional form of oscillator-multiplier, the low-potentialend of inductance coil is either connected directly to thegroundeds-ides; of capacitors 2 and/or 3, orisgroundeddirectly,

- as for example,-to thechassis. Similarly, inthe conventional circuit,the tapped connection-pf coil 5 is either connected directly ,to cathodell. or grounded directly, as to the chassis.

I have found, however, thatthe output voltage. v of a high frequencydoubleroramul-tiplier,canbe substantially increased, and in additionheldarelai ti-vely constant in amplitudepver the required high frequencyrange, :by connecting the low :po-u

tential end .ofcoil vll and also the tapped tonnes-- I tion 24 of;coi-1;5 toa tapped poi t. go @519 potential endof coil 9. In Figure 1,these connections are made byway of conductor 25. The tapped connection26 is preferably made very close to ground. Inthe actual construction ofthe particular high frequency oscillator-multiplier illustrated inFigure 1, the tapped connection 26 is made to the upper end of groundlug 8which connects coil 9 to the chassis. It will be understood that atthe high frequencies involved the .inductance of lug 8 is appreciableand that lug 8 functions as a portion of coil 9. The physical dimensionsof lug 8 were such that the ungrounded end thereof was approximatelythree-eighths of an. inch removed from-the chassis. I have found thatthe position of the tapped-connection is most. critical; for example, iftap 26 is moved to any appreciable extent either closer to or fartheraway from chassis (ground) than the end of lug 8, the improvements inthe amplitude and uniformity of the multiplier output voltage rapidlydiminish. Of'course the optimum adjustment will vary in differentarrangements, depending upon-the physical size of the structuresinvolved. v

I have also observed that the direction of winding of coil 4 has abearing upon the results achieved. With the Winding in one direction,the optimum improvements in multiplier output voltage are obtained; ifthe winding be reversed the improvements may not be realized. Whichdirection of winding is productive of the most favorable results may bereadily determined by trial.

Reference is now made to Figure 2 wherein curves representing the outputvoltage of the frequency multiplier are plotted against frequency, bothfor the conventional circuit and also for the novel circuit organizationembodying the invention illustrated in Figure 1. Curve A of Figure 2represents the output voltage characteristic of the frequency multiplierwhen the conventional form of circuit hereinbefore described is used.Curve B is the output voltage curve obtained when the novel arrangementsof Figure 1 are employed. It will be observed that, with the exceptionof the extreme low-frequency end, the magnitude of the output voltagerepresented by curve B is much greater than that shown by curve A. Itwill be noted also that the voltage variations within the band '78 to100 me. are negligible in curve B as compared with those of curve A.Curve B therefore represents a very important improvement over theconditions shown in curve A.

The precise theory of operation of the improved circuit has not beendefinitely established. It will be appreciated by those skilled in theart that, at the very high frequencies here under consideration, strayinductances and stray capacitances existing throughout the circuitssubstantially affect the operation of the apparatus. These effects maybe quite different at different frequencies in the operating range. Forexample, a particular, physically small portion of circuit may be seriesresonant at one frequency, and parallel resonant at a differentfrequency within the same operating band, and in consequencesubstantially affect the output voltage of the multiplier, or of theoscillator, or of both.

The circuit organization illustrated in Figure 1, which substantiallyimproves the output voltage characteristics of theoscillator-multiplier, provides coupling means for feeding back highfrequency energy from the output circuit of the multiplier to the plateand/or grid circuits of the oscillator, the phase relations apparentlybeing such that increased signal voltageon grid l6 of the multiplier isrealized, thereby producing increased output.

. If desired, only tap 24 of coil 5 may be connected to tap 26 of coil9, the connection of thelow potential end of coil 4 to tap 26 beingomitted, and connection thereof made. directly to the grounded sides ofcapacitors 2 and/or 3, or to chassis (ground) in the conventionalmanner.

Or, theabove connections may be reversed, that is, the low potential endof coil 4 may be connected to tap 26 of coil 9, tap 24 of coil 5 beingconnected in the conventional manner directly to chassis (ground) ordirectly to cathode H.

I found that if the preferred circuit illustrated in Figure 1 ismodified in either of the above manners, the output voltagecharacteristic of the multiplier is appreciably improved over that ofthe conventional circuit insofar as uniformity of output over thefrequency band is concerned; but substantially increased amplitude ofoutput is not realized.

I have described and illustrated my invention by means of anoscillator-multiplier which uses a single dual purpose vacuum tube, butit will be understood that the invention is also applicable to thecombination of an oscillator and frequency multiplier in which separatevacuum tube envelopes are employed. Moreover, the invention is notlimited to the particular form of oscillator circuit shown in theillustration; any of the oscillator circuits known to be suitable forthe generation of high frequency oscillations, of the order and for thepurposes here involved, may be employed.

Having described my invention in a preferred form, but intending to belimited only by the scope of the claims, I claim:

1. In combination, a high frequency oscillator comprising a tube havingcathode, plate and grid electrodes, said oscillator including a tunablefrequency-determining network and plate-cathode and grid-cathodecircuits, a frequency multiplier having an output circuit tunable to aharmonic of the oscillator frequency, means for applying the oscillatoroutput to the multiplier, and means for applying a portion of the outputof said multiplier to the grid-cathode circuit of the oscillator.

2. In combination, a high frequency oscillator comprising a tube havingcathode, plate and grid electrodes, said oscillator including a tunablefrequency-determining network and plate-cathode and grid-cathodecircuits, at frequency multiplier having an output circuit tunable to aharmonic of the oscillator frequency, means for applying the oscillatoroutput to the multiplier, and means for applying a portion of the outputof said multiplier to the plate-cathode and gridcathode circuits of theoscillator.

3. In combination, a high frequency oscillator comprising a tube havingcathode, plate and grid electrodes, said oscillator including a tunablefrequency-determining network inductively coupled to the grid-cathodeand plate-cathode circuits of said oscillator, a frequency multiplierhaving an output network tunable to a harmonic of the oscillatorfrequency, means for applying the oscillator output to the multiplier,and means for applying a portion of the multiplier output to thefrequency-determining network of the oscillator.

4. In a high frequency oscillator-multiplier having an oscillatorsection which includes a tube having cathode, plate and grid electrodesswe tie and-a. tunable frequency-determining network inductively coupledto the grid-cathode and plate-cathode circuits of said oscillator andhawing: a multiplierv s'ectionwhich includes .an. output networktunaloletov a harmonicofthe oscillator frequency; means for applying aportion of; the multiplier outputto the grid-cathode circuitoi theoscillator and to. the oscillators frequencydetermining network, saidmeans comprisinga connection from the multiplier. output. network to theoscillators frequencyedetermining network and grid-cathode circuit.

5; An oscillator-multiplier including two triodes in a single vacuumtube envelope, the multiplier portion comprising one of said :triodes.and a frequency-determining output circuit including an inductance, theoscillator portioncomprising the other of said triodes andplate-cathndev and grid-cathode circuits including a tunablefrequency-determining network, said grid-cathode cathode-andgrid-cathode circuits incIudinefl/a tunable; frequcnwdetermining;networkgrssaid grid-cathadecircuit: including. a tannednortiQ of .saiduzdouhler output.inductance;saidetapped portionwheing avportion: of the: low potential tvid of said doubler, inductance.-

'7. An. voscillator-doublenz including a double triodez vacuum tube;wsaid doublet; portion nris ng ne ofvsaid ,triodes.;.a-nd-a -tunablquency detemliningputnut circuit includin' inductance" coil; aidoscillator: pontionscompris ingrthe. other :ofzsalid-etriodes zaplatereathflqe circuit, a -griclrcathode circuitpandwa tunableirequencyeidetermining network-inductively cou-A v pledto saidplateecathode: andv gridecathodeacire:

.cuits', saidlgridecathode circuitincludinge tapped portion of-.1 saiddoubler: output: inductance c'oil said tapped-- portion comprising aportion-loft the low potential end. of-::said: doubler. output induct-sance coil.

I PJ'BUFFINGTGNi BEFEBENGEMIIE a The following references are oi recordrinfthe' Number I Name I 2,193,491 Reinartz; e- Marl Ii2,"-'-194Q .17.

wee e b r sen w?"

